A definition enhancement technology can improve signal detail, and has been widely applied to the signal processing field currently. However, when a prior-art definition enhancement method is used to process a signal, an overshoot phenomenon is likely to occur, reducing signal quality. As shown in FIG. 1, 101 represents a waveform of an original signal, 102 represents a signal waveform obtained after definition enhancement processing has been performed on the original signal, and the signal waveform obtained after the processing includes an upward protrusion 103 and a downward protrusion 104, that is, an overshoot phenomenon occurs.
To suppress an overshoot phenomenon, an image quality improvement device is proposed in the prior art. Referring to FIG. 2, the image quality improvement device includes a first differentiating circuit 201, a second differentiating circuit 202, a multiplier 203, an adder 204, and a minimum/maximum filter 205. After an original signal is input to the first differentiating circuit 201 and the second differentiating circuit 202, the first differentiating circuit 201 generates a first derivative signal of the original signal, the second differentiating circuit 202 generates a second derivative signal of the original signal, the multiplier 203 multiplies the first derivative signal by the second derivative signal to generate a sharpness correction signal, the adder 204 adds the original signal and the sharpness correction signal to generate a signal on which definition enhancement processing has been performed, and the minimum/maximum filter 205 detects and filters the signal on which definition enhancement processing has been performed to control an overshoot amplitude of a corrected signal.
The prior art has the following disadvantages:
When a signal is processed by using the foregoing image quality improvement device, processing effects on signals of different amplitudes are different, resulting in an unnatural processed image. That is, a small-amplitude signal has a smaller definition enhancement extent compared with a large-amplitude signal, or a large-amplitude signal has a larger definition enhancement extent compared with a small-amplitude signal. In addition, the foregoing processing method for controlling an overshoot amplitude of an output signal also results in an unnatural processed image.